The invention relates to a method and a tool for producing a plastic component comprising a decorative layer and a backing layer and an additional molded part.
The component to be produced is, in particular, a plastic component comprising fiber fractions.
The additional molded part is attached to the rest of the component that is produced; and it is defined below, in particular, as an attachment, a retainer element, a receiving element, a reinforcing element or a rib or also, in general, as an additional component, which is to be integrated on the back side of the component.
In the prior art production of plastic components comprising a plurality of layers and additional molded parts, which are attached to said plastic components, the first step is to produce the component, comprising a backing layer and a decorative layer, with a compression molding tool in a laminating and contour-shaping process. In a second step the additional molded part is attached by injection molding or adhesive bonding or welding to the component. Such production processes need to be improved.
In contrast, plastic components, comprising a backing layer and a decorative layer, can also be produced by an injection molded backing process. In this case a decorative material is placed into an injection molding tool, and a thermoplastic material is injected behind the decorative material. This thermoplastic material solidifies upon cooling. In the production of molded parts using an injection casting tool, the molded parts can be produced in a single step or in multiple steps.
For example, EP 0 371 425 B1 discloses a two-step method. According to this method, a film material, which is provided as a decorative layer, is thermoformed and deep-drawn; and in a subsequent process step it is placed into an injection casting tool and is provided with an injection molded backing of a thermoplastic. However, this method is suitable only for simply shaped molded parts.
Furthermore, EP 0 320 925 A1 discloses a method, in which the decorative material is placed into the injection casting tool. Then a thermoplastic is injected behind the decorative material at 10 to 130 bar. Thus, the decorative material is then molded by the pressure of the thermoplastic material and is pressed into the injection casting mold. Even with this method only relatively simply shaped molded parts can be produced.
According to DE 197 29 780 C1, sliders were also used for producing moldings having complicated shapes. The movement of these sliders ensures that the injection casting material is pressed into all regions of the injection casting mold. However, this measure has proved to be very disadvantageous because it leads to wrinkling and damage to the decorative surface. Furthermore, the decorative layer is pressed so flat that a decorative embossing is no longer possible.
The slider is moved on the rear-sided tool half to that point of the backing element, at which the attachment is supposed to be produced. This position is simultaneously the contour-shaping position of the attachment. Then polypropylene is injected into the tool region from an injection point at an injection pressure ranging usually from 150 to 350 bar. The use of such a high pressure is necessary, inter alia, because the thin material gap in the tool for contour-shaping the attachment has to be filled entirely with the polypropylene. Therefore, a slider is moved first into position; and then the tool gap or the injection gap is filled with polypropylene. One drawback with this method is that the wall thickness of the attachment is relatively low at the transition region to the backing element so that, as a result the bonding area at this point is negligible.
The injection takes place just after the tool is closed, so that the fiber mat has not cooled down yet. That is, the material is still plasticized and, thus, soft. Furthermore, at a high injection pressure marks form on that side of the backing element and/or the fiber mat that is opposite the side of the attachment owing to the softness of the component. This side is usually covered with decorative material so that these marks constitute a drawback for the aesthetic appearance.
In order to avoid these problems, DE 197 29 780 C1 proposes a solution for manufacturing complicated molded parts, wherein the decorative material is placed in an injection molding tool, which is pressurized with gas while the tool is closed so that the decorative material is pressed into the cavities of the injection molding tool, and then the plastic is injected behind the decorative material. Owing to the uniform pressure distribution in the tool, a homogeneous pressing of decorative material into the cavities of the injection mold is achieved.